Remifentanil is a opioid receptor agonist which is rapidly metabolized by nonspecific tissue and plasma esterases. As with all drugs in the fentanyl class of opioids, remifentanil is gaining widespread use in infants and children. Remifentanil is a particularly appealing opioid for use as an anesthetic agent, given its rapid onset and short duration of action. To date, however, there is no data available describing the pharmacokinetcs (PK) of remifentanil in infants. We are currently studying this in 12 infants undergoing surgery under general anesthesia, including a continuous infusion of remifentanil. As the infusion is adjusted according to signs of the depth of anesthesia, blood samples are drawn and immediately processed for assay.